Help! New Gitzo head to attach to older model tripod

[chonbhoy]

I bought a new ball head for my Gitzo traveller series 2 tripod and i'm wondering what is required to attach it as it has a larger base and the old head has a captive screw for attaching it to the centre column head on the series 2. The new head only has a threaded hole.
The head is GH2780QR and the tripod is GK2580TQR.
I've done plenty searching but all i've been able to work out is that I might only need this >> Gitzo GS2320D Series 2 Aluminium Power Disc.
I'm unsure though.